Chemical vapor deposition methods are employed to form films of material on substrates such as wafers or other surfaces during the manufacture or processing of semiconductors. In chemical vapor deposition, a chemical vapor deposition precursor, also known as a chemical vapor deposition chemical compound, is decomposed thermally, chemically, photochemically or by plasma activation, to form a thin film having a desired composition. For instance, a vapor phase chemical vapor deposition precursor can be contacted with a substrate that is heated to a temperature higher than the decomposition temperature of the precursor, to form a metal or metal oxide film on the substrate. Preferably, chemical vapor deposition precursors are volatile, heat decomposable and capable of producing uniform films under chemical vapor deposition conditions.
The semiconductor industry is currently considering the use of thin films of various metals for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films. A need exists in the industry for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions.
For chemical vapor deposition and atomic layer deposition applications, a variety of precursors (amides, alkoxides, and chlorides) exist for a variety of elements (e.g., titanium, hafnium, and tantalum). The chemistry of these materials is dominated mainly by homoleptic systems, or complexes with ligand sets made up of one or more identical ligands, for example, tetrakis(dimethylamino)titanium or tetrakis(ethylmethylamino)hafnium. In contrast, heteroleptic systems for this type of material would consist of two or more different ligands, for example, bis(dimethylamino)bis(ethylmethylamino)-hafnium.
Materials with heteroleptic ligands within the same family can be difficult to prepare and purify. The difficulty in preparing and purifying these heteroleptic systems stems from their rapid reactivity, ligand exchange potential, and similar vapor pressures. For example, combining 2 equivalents of amide ‘A1’ with HfCl4 will typically not lead to exclusively Hf(A1)2(Cl)2, but instead will lead to a range of statistically distributed Hf(A1)x(Cl)4-x species (where x=0-4). Therefore, even if a second amide ‘A2’ is added well after the first, a mixture of compounds of the formula Hf(A1)x(A2)4-x (where x=0-4) will result. These compounds, due to their similarity, are difficult to isolate cleanly, even by distillation.
In developing methods for forming thin films by chemical vapor deposition or atomic layer deposition methods, a need continues to exist for precursors that preferably are liquid at room temperature, have adequate vapor pressure, have appropriate thermal stability (i.e., for chemical vapor deposition will decompose on the heated substrate but not during delivery, and for atomic layer deposition will not decompose thermally but will react when exposed to co-reactant), can form uniform films, and will leave behind very little, if any, undesired impurities (e.g., halides, carbon, etc.). Therefore, a need continues to exist for developing new compounds and for exploring their potential as chemical vapor and atomic layer deposition precursors for film depositions. It would therefore be desirable in the art to provide precursors that possess some, or preferably all, of the above characteristics.